That's because taxes go into the consolidated fund - it's a long standing principle (common to all political parties) that taxes are never directly allocated to particular programmes.
Charging mechanisms are different, and in this case it would be more likely to be constituted as a charge for a licence to operate - something that is an optional service (i.e. you don't have to operate a brothel, unlike say income tax which you have to pay). Charges can, but do not have to, be routed direct to a particular programme.